"As soon as they put in the gates on Flinders Street and the boom gate on last Monday, that was it for us," Mr Hall-Haydon said.

He said he didn't want to rush into "jumping up and down over nothing".

"But as it has turned out, it has been really bad."

Businesses say the closure of part of Flinders Street is hitting them hard.Credit:Justin McManus

Mr Hall-Haydon said he was already looking at losing staff, most of whom have been there since Tulip Coffee opened two years ago.

"I feel they’ve become part of the family and all of a sudden you have to do that to them, which doesn't feel good."

Flora Indian Restaurant, cornered by construction opposite Flinders Street Station, is already looking at cutting five staff including two full time workers after being in business for 20 years.

The son of the owners, who asked to be known as PK, said the restaurant had lost as much as 50 per cent of its business.

"What really gets us going is the fact there's no compensation."

PK said Metro Tunnel had offered marketing and social media support to boost the restaurant's business, but his family would look at legal action if they were not offered financial compensation.

"It's bits and bobs. That doesn't bring back that 50 per cent we've lost," he said.

PK outside his parents' Flora Indian Restaurant.Credit:Rachel Eddie

"Flinders Street is what it is because of foot traffic. When you chop it in half, it changes the whole demographic of who comes through."

He said it was possible business could improve again over time.

At neighbouring Out of the Closet Vintage Clothing store, manager Claire Powell said business dropped up to 70 per cent "virtually overnight".

The owners, who were planning to retire after 21 years in business, are now looking to cut staff and may have to return to work themselves.

CT Mart convenience store, which only opened in June, has also suffered despite vouchers that Metro Tunnel has provided to entice customers.

"It's really bad. Really, really bad," Julia Ting said.

She noted the other businesses were surviving off regulars, but tourists don't "search around the city" for a convenience store.

The nine-kilometre Metro Tunnel, which is expected to be finished in 2025, will run under the city between South Kensington and South Yarra. Once complete, the $11 billion tunnel will join the Cranbourne-Pakenham and Sunbury train lines, and include five new underground stations: North Melbourne, Parkville, State Library, Town Hall and Anzac.

A Rail Projects Victoria spokesman said the work on Flinders Street was vital in order to build a passenger connection between the new Town Hall Station and Flinders Street Station, "and to improve community safety by reducing the number of trucks during construction on Swanston Street".

He said the Metro Tunnel Project was "in regular contact with the businesses".

"We’re acutely aware it’s a challenging time for some in the area and we’re keeping businesses informed and supported.

"Metro Tunnel staff are also on site handing out vouchers to encourage shoppers to stay in the area. We are working with individual businesses on a number of other support measures including marketing and promotion and activation opportunities."

On Wednesday, Opposition Leader Michael O'Brien said the closure was having a "crushing affect on small business".

"Daniel Andrews and Labor can’t manage money, can’t manage major projects and as a result, small businesses and their workers are forced to pay the price," Mr O'Brien said in a statement.

However, at Mock Turtle cafe on Degraves Street on Wednesday afternoon staff said they did not think there had been a dip in customers.

Waitress Claudia Karlos said Metro had been "super accommodating" and people would adapt.

Jeremy Pannell, who was manning the bar at Il Tempo Pizza and has worked there for three years, said the construction works were "negative" and there had been no consultation.